1. Field of the Invention
The present invention relates to an image forming apparatus. More specifically, the present invention relates to an image forming apparatus that has a feed roller and a press roller.
2. Background Information
Heat transfer printers and other such image forming apparatuses that have a feed roller and a press roller are well known. FIG. 14 is a perspective view showing the entire configuration of an example of a conventional heat transfer printer. FIG. 15 is a plan view of the conventional heat transfer printer shown in FIG. 14. FIGS. 16 through 19 are diagrams for describing the structure of the conventional heat transfer printer shown in FIG. 14. The structure of the conventional heat transfer printer will now be described with reference to FIGS. 14 through 19.
As shown in FIGS. 14 and 15, a conventional heat transfer printer has a metal chassis 101, a metallic feed roller 102 for feeding paper, a metallic press roller 103 for coming into contact with the feed roller 102 with a specific amount of pressure, a separating member 104, a resinous feed roller bearing 105 for rotatably supporting the feed roller 102, a resinous press roller bearing 106 for rotatably supporting the press roller 103, a feed roller gear 107 mounted on the feed roller 102, a metallic press arm 108, a tension coil spring 109, a motor 110 for driving the feed roller 102 and the like, a thermal head 111 for printing, a platen roller 112, a resinous platen roller bearing 113 for rotatably supporting the platen roller 112, a pressing member 114, a torsion coil spring 115, a motor 116 for driving the thermal head 111, an ink sheet take-up gear 117, a roller axle 118, a rubber paper supply/eject roller 119 mounted on the roller axle 118, a roller axle gear 120 mounted on the roller axle 118, a motor bracket 121, a drive gear 122, and intermediate gears 123, 124, and 125.
As shown in FIG. 14, the aforementioned motor bracket 121 is mounted on the first side surface 101a of the chassis 101. Also, an ink sheet insertion part 101c through which ink sheets (not shown) are inserted is provided to the second side surface 101b of the chassis 101. A spring mounting hole 101d in which one end of the tension coil spring 110 is mounted is formed in the second side surface 101b of the chassis 101.
The feed roller 102 has a bearing support portion 102a on the side of the chassis 101 with the first side surface 101a, a bearing support portion 102b on the side of the chassis 101 with the second side surface 101b, a gear insertion part 102c, and a paper conveying unit 102d, as shown in FIG. 16. The bearing support portions 102a and 102b of the feed roller 102 have a smaller diameter than that of the portion of the feed roller 102 between the bearing support portions 102a and 102b. Also, the bearing support portions 102a and 102b are rotatably supported on feed roller bearings 105. The feed roller bearings 105 are mounted using screws 126 on the first side surface 101a and second side surface 101b of the chassis 101, as shown in FIGS. 18 and 19. The gear insertion part 102c on the outer side of the bearing support portion 102a fits into the insertion hole 107a in the feed roller gear 107 so as not to be relatively rotatable. Also, convex portions having a predetermined height are formed by the roll-forming on the surface of the paper conveying portions 102d of the feed roller 102, as shown in FIG. 16. The paper conveying portion 102d is a portion of the surface of the feed roller 102 where the convex portions are formed.
As shown in FIG. 16, the bearing support units 103a and 103b of the press roller 103 have a smaller diameter than the portion of the press roller 103 between the bearing support portions 103a and 103b. Metallic separating members 104 that have a greater diameter than the press roller 103 is mounted on the bearing support portions 103a and 103b of the press roller 103. The separating members 104 come into contact with the outermost peripheral surface of the feed roller 102 so as to prevent the distal end of the convex portions on the paper conveying unit 102d of the feed roller 102 from coming into contact with the press roller 103. Press roller bearings 106 are mounted on the press arm 108 provided to the inner side of both the first side surface 101a and the second side surface 101b of the chassis 101. The press arms 108 are mounted on the first side surface 101a and the second side surface 101b of the chassis 101 so as to be capable of pivoting around the support unit 108a, as shown in FIG. 14. The first end of the tension coil spring 109 for urging the press roller 103 to press on the feed roller 102 is mounted in the spring mounting hole 110d of the chassis 101. The second end of the tension coil spring 109 is coupled to a spring mounting part 108b of the press arm 108.
The thermal head 111 is coupled to the inner sides of the first side surface 101a and second side surface 101b of the chassis 101 to be capable of pivoting around a supporting axle 111a, as shown in FIG. 14. The torsion coil spring 115 is coupled to the supporting axle 111a, as shown in FIG. 15. The torsion coil spring 115 urges the thermal head 111 in a direction away from the platen roller 112 (direction of the arrow F in FIG. 14). Also, when the thermal head 111 receives the driving force from the motor 116 transmitted via the drive gear 122 and the pressing member 114, and therefore pivots in the direction of the arrow E in FIG. 14 and presses on the platen roller 112.
The platen roller 112 has a bearing support portion 112a on the side of the first side surface 101a of the chassis 101, and a bearing support portion 112b on the side of the second side surface 101b of the chassis 101, as shown in FIG. 17. The bearing support portions 112a and 112b are rotatably supported on the platen roller bearings 113. The platen roller bearings 113 are mounted by screws 126 on the first side surface 101a and the second side surface 101b of the chassis 101, as shown in FIGS. 18 and 19.
The driving force from the motor 110 is transmitted to the feed roller gear 107 via the intermediate gear 123, as shown in FIGS. 14 and 15. The motor 110 is mounted on the motor bracket 121. The motor 110 also functions as a drive source for driving the feed roller 102, the ink sheet take-up member (not shown), and the roller axle 118. The feed roller gear 107 engages the intermediate gears 123 and 124. The intermediate gears 124 transmit the driving force from the feed roller gear 107 to the ink sheet take-up gear 117 fitted over the ink sheet take-up roller (not shown). The intermediate gears 124 also transmit the driving force from the feed roller gear 107 to the roller axle 118 on which the paper supply/eject roller 119 is mounted via the roller axle gear 120.
The relationship between the positions of the feed roller 102, the press roller 103, and the paper 127 in this heat transfer printer will now be described with reference to FIGS. 15 and 16. In FIGS. 15 and 16, the center position of the paper 127 in the width direction (the direction of the arrow X in FIG. 15), which is orthogonal to the conveyance direction (of the arrow Y in FIG. 15) of the paper 127, is denoted by L4, the center position (center line) of the distance between the feed roller bearings 105 is denoted by L5, and the center position (center line) of the distance between the press roller bearings 106 is denoted by L6.
Furthermore, the distal position of the feed roller bearing 105 mounted on the first side surface 101a side is denoted by P3, and the distal position of the feed roller bearing 105 mounted on the second side surface 101b side is denoted by P4. The feed roller 102 is rotatably supported on the feed roller bearings 105 mounted on the first side surface 101a and the second side surface 101b of the chassis 101, as shown in FIGS. 15 and 16. The center position L5 between the position P3 of the feed roller bearing 105 mounted on the first side surface 101a and the position P4 of the feed roller bearing 105 mounted on the second side surface 101b is thereby the center position of the distance between the first side surface 101a and the second side surface 101b of the chassis 101.
As shown in FIG. 15, the center position L4 of the width direction of the paper 127 (the direction of the arrow X in FIG. 15), which is also the center of the paper conveying unit 102d, is displaced toward the second side surface 101b of the chassis 101 relative to the center position of the distance between the first side surface 101a and second side surface 101b of the chassis 101 or the center position L4 because the drive gear 122 that drives the pressing member 114 for pressing on the thermal head 111 is disposed on the inner surface of the first side surface 101a. In other words, the center position L5 of the distance between the pair of feed roller bearings 105 does not match the center position L4 of the paper 127.
Also, as shown in FIG. 16, the press roller 103 is rotatably supported by the press roller bearings 106 mounted on the press arms 108 that are provided to the inner sides of the first side surface 101a and second side surface 101b of the chassis 101. As shown in FIG. 16, the center position L6 of the distance between the press roller bearings 106 substantially coincides with the center position L5 of the distance between the feed roller bearings 105, but does not coincide with the center position L4 of the paper 127.
Next, the operation of feeding paper 127 in the heat transfer printer according to the conventional example will be described with reference to FIGS. 14 and 15. In the feed operation of the conventional heat transfer printer 127, the driving force of the motor 110 is transmitted to the feed roller gear 107 via the intermediate gear 123, as shown in FIGS. 14 and 15. The feed roller 102 thereby rotates. The driving force of the motor 110 is transmitted from the feed roller gear 107 to the ink sheet take-up gear 117 via the intermediate gear 124, and the ink sheet (not shown) is therefore rolled. The driving force of the motor 110 is also transmitted from the feed roller gear 107 to the roller axle gear 120 via the plurality of intermediate gears 124, and the paper 127 therefore is conveyed in the paper supply direction or the paper ejection direction.
During the printing operation, the thermal head 111 is pivoted in a direction in which pressure is applied to the platen roller 112 (the direction of the arrow E) by the motor 116. When the paper is conveyed in the opposite direction (the direction of the arrow H), the thermal head 111 pivots in a direction away from the platen roller 112 (the direction of the arrow F). As a result, during the printing operation, the paper 127 is held between the thermal head 111 and the platen roller 112 and is conveyed forward (in the direction of the arrow G) by the feed roller 102 and the press roller 103. As the paper 127 is to be conveyed in the opposite direction (the direction of the arrow H), the paper 127 is conveyed while being held between the feed roller 102 and the press roller 103.
In the conventional printer shown in FIGS. 14 through 19, there is no match between the center position L4 of the paper 127, the center position L5 between the feed roller bearings 105, and the center position L6 between the press roller bearings 106. As a result, there is no match between the center position L4 of the paper 127 and the center position L6 between the points in which pressure is applied to the feed roller 102 by the press roller 103 (positions in which pressure is applied by the press arms 108). The pressure applied to the paper 127 by the press roller 103 is thereby not uniform in the transverse direction, and the paper 127 tends to be conveyed in a direction not orthogonal to the width direction of the paper 127. As a result, the precision with which the paper 127 is fed is therefore compromised.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved image transfer apparatus that overcomes the problems of the conventional art. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.